bpf, riscv64: Introduce emit_load_*() and emit_store_*()

bpf, riscv64: Introduce emit_load_*() and emit_store_*()

We're planning to add support for the load-acquire and store-release
BPF instructions.  Define emit_load_<size>() and emit_store_<size>()
to enable/facilitate the (re)use of their code.

Acked-by: Björn Töpel <bjorn@kernel.org>
Reviewed-by: Pu Lehui <pulehui@huawei.com>
Tested-by: Björn Töpel <bjorn@rivosinc.com> # QEMU/RVA23
Tested-by: Peilin Ye <yepeilin@google.com>
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
[yepeilin@google.com: cosmetic change to commit title]
Signed-off-by: Peilin Ye <yepeilin@google.com>
Link: https://lore.kernel.org/r/fce89473a5748e1631d18a5917d953460d1ae0d0.1746588351.git.yepeilin@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>